It is known to provide fluid sampling devices using optical near-field imaging as disclosed in U.S. Pat. No. 5,572,320, which is incorporated herein by reference. Such a device is employed to determine the quantity, size, characteristics, and types of particulate matter in fluids. Examples of fluids which are monitored in such a system are lubricating oils used in engines and rotating machinery; hydraulic fluid used in various machinery; and fluids used in industrial quality control, food processing, medical analysis, and environment control. In its most common use, such a device monitors engine oil for metal particulates or flakes, wherein a size, number, and shape of particulates correspond to an engine condition and can alert one to particular problems with the engine. Non-metallic debris in the fluid can also be detected, such as fibers, sand, dirt and rust particles. Predicting failure is critically important in aircraft engines to avoid accidents and loss of life.
The early stages of engine wear cause small particulate matter, of about 50 microns or less in size, to be generated. These particulates have characteristic shapes indicative of the type of wear produced by specific wear mechanisms. As the wear process progresses, the amount and size of particulates increase. Accordingly, imaging and identifying smaller particles allows early identification of faults, thus, allowing more time for corrective maintenance and preventing unexpected catastrophic failures.
The advantage of the aforementioned system over previous systems is readily apparent when one considers that the previous systems only measured the amount of light passing through the material-laden oil, but gave no consideration as to the particular shape of the material. As best seen in FIGS. 1A-G, the various types of images rendered by a known system can provide a clear indication of the types of problems that are likely to occur based upon the shape and structure of the debris monitored. For example, in FIG. 1A, sliding wear particles are shown and these particles are believed to be caused by metal-to-metal contact due to overloading, misalignment, low speed and/or low oil viscosity. The debris shown in FIG. 1B represents fatigue wear particles which are gear or bearing pieces generated due to surface stress factors such as excessive load, contamination, and the like. FIG. 1C shows cutting wear particles that are generated by surface gouging, two body cutting due to break-in, misalignment, and three body cutting due to particle abrasion. FIG. 1D shows oxide particles which are caused by contamination, and red oxide caused by water or insufficient lubrication of the subject machinery.
It will also be appreciated that certain elements may be in the oil that generates false readings. These elements are classified and can be disregarded by the imaging system. For example, as shown in FIG. 1E, fibers are shown which are normally occurring or may be caused by improper sample handling. Instrument problems due to incomplete removal of air bubbles are represented in FIG. 1F. Finally, FIG. 1G shows flow lines which are a result of instrument problems caused by insufficient mixing of a new sample.
In order for such an imaging system to work properly, the system must allow for proper focusing so that the field of view of the fluid to be imaged is within at least plus or minus 20 microns. The debris-containing fluid is pumped through an optical flow cell which is typically held in a fixed position. A laser light illuminates one side of the flow cell and a camera is positioned on the other side. The flow cell is movably positioned to obtain a proper focus. Accordingly, U.S. Pat. No. 6,104,483, which is incorporated herein by reference, facilitates positioning of a flow cell by using a defined reference flange. Although this optical flow cell improves the system's performance, positioning of the other components in the imaging system has been found to be lacking in prior art equipment. In other words, if the other components of the system used to image the fluid passing through the optical flow cell are not properly positioned and aligned, the image obtained by the system may be distorted or, in the worst case, not detected at all.
Previous fixtures employed a camera mounted on a slide device that was incrementally moved until a desired focus was obtained. This position was held in place by tightening screws associated with the slide device. As will be appreciated, tightening the screws slightly adjusts the position of the camera, which may result in the camera being removed from the desired focus. Previous imaging fixtures also required access to both the top and bottom of a plate which supported the slide and other system components. Accordingly, making fine adjustments to the positioning of the camera and the optical flow cell were found to be quite cumbersome and, as a result, performance of routine maintenance on the device was found to be quite difficult. The previous fixture was also problematic in that all of the important components were moveable upon the holding plate and, as such, obtaining a proper focus for the camera was quite difficult. Therefore, there is a need in the art for optical debris analysis fixture which requires minimal adjustment of focus and which allows for simple replacement of the optical flow cell while maintaining focus.